Method of producing chlorine dioxide using sodium chlorite and a water-retaining substance impregnated in zeolite or in aqueous solution

ABSTRACT

A method for producing chlorine dioxide by activating zeolite crystals (which have been impregnated with metal chlorite such as sodium chlorite, and optionally also a water-retaining substance such as magnesium sulfate, potassium chloride, potassium hydroxide, or calcium chloride) with excess protons, or activating an aqueous solution of metal chlorite and such a water-retaining substance with excess protons. Proton generating species useful for the activation are acids such as acetic, phosphoric, and citric acid, and metal salts such as ferric chloride, ferric sulfate, ZnSO 4 , ZnCl 2 , CoSO 4 , CoCl 2 , MnSO 4 , MnCl 2 , CuSO 4 , CuCl 2 , and MgSO 4 . The activation can be performed by causing fluid to flow through a bed of zeolite crystals impregnated with calcium chloride (or other water-retaining substance) and sodium chlorite, and a bed of zeolite crystals impregnated with a proton generating species. The two beds can be physically mixed together or the fluid can flow sequentially through separate beds. The activation can also be performed by immersing impregnated zeolite crystals in (or spraying them with) acid or another proton generating species. To produce chlorine dioxide using a sodium chlorite-containing aqueous solution, the solution can be mixed or otherwise combined with acid. Other aspects of the invention are impregnated zeolite crystals (or other carriers) which are useful for producing chlorine dioxide and are stable until activated with protons. Presence in a sufficient amount of a water-retaining substance in the unactivated material reduces the rate of chlorine dioxide outgassing to no more than a negligible amount prior to activation.

CROSS-REFERENCE TO RELATED-APPLICATION(S)

[0001] This is a continuation-in-part application of pending U.S.application Ser. No. 08/798,873, filed Feb. 11, 1997, scheduled to issueas U.S. Pat. No. 5,885,543 on Mar. 23, 1999, and entitled “Method forProducing Chlorine Dioxide Using Calcium Chloride Impregnated Zeolite orAqueous Calcium Chloride”, inventor Fred Klatte.

FIELD OF THE INVENTION

[0002] The invention relates to methods for producing chlorine dioxide,and to substances used in performing such methods. Each method produceschlorine dioxide by activating zeolite crystals (previously impregnatedwith a mixture of sodium chlorite and a water-retaining substance suchas calcium chloride) with protons (from an acid or other protongenerating species), or by activating an aqueous solution of awater-retaining substance (such as calcium chloride) and sodium chloritewith protons (from an acid or other proton generating species).

BACKGROUND OF THE INVENTION

[0003] Zeolites are hydrated metal aluminosilicate compounds withwell-defined (tetrahedral) crystalline structures. Because zeolitecrystals (both natural and synthetic) have a porous structure withconnected channels extending through them, they have been employed asmolecular sieves for selectively absorbing molecules on the basis ofsize, shape, and polarity.

[0004] Volumes packed with zeolite crystals (for example, small zeolitecrystals chosen to have size in the range from 0.2 mm to one quarterinch) have been employed in air (or other gas) and water filtrationsystems to selectively absorb contaminants from a flowing stream ofwater or gas.

[0005] U.S. Pat. No. 5,567,405, issued Oct. 22, 1996 (based on U.S.application Ser. No. 08/445,025, filed May 19, 1995), and U.S. Pat. No.5,573,743, issued Nov. 12, 1996 (based on U.S. application Ser. No08/445,076), teach methods for producing zeolite crystals impregnatedwith one or more of sodium chlorite, acetic acid, phosphoric acid, andcitric acid, and methods for producing chlorine dioxide by moving afluid (e.g., air or water) relative to a bed of zeolite crystalsimpregnated with sodium chlorite, and moving the fluid relative toanother bed of zeolite crystals impregnated with one of the following:phosphoric acid, acetic acid and citric acid. The two beds can bephysically mixed together, or the fluid can flow sequentially throughdistinct first and second beds. These references also teach a method forfiltering a fluid by producing chlorine dioxide in the fluid (in themanner described in this paragraph) and then absorbing the chlorinedioxide from the fluid.

[0006] U.S. patent application Ser. No. 08/704,086, filed Aug. 28, 1996,teaches a variation on the chlorine dioxide production method of U.S.Pat. No. 5,567,405, which includes the steps of moving a fluid through afirst bed of impregnated zeolite crystals (impregnated with at least oneof phosphoric acid, acetic acid, and citric acid) and then moving thefluid through a second bed of impregnated zeolite crystals (impregnatedwith sodium chlorite).

[0007] Chlorine dioxide (ClO₂) is useful for killing biologicalcontaminants (such as microorganisms, mold, fungi, yeast and bacteria)and for oxidizing volatile organic chemicals which can contaminatefluid.

[0008] It is known to produce chlorine dioxide by: activating a metalchlorite solution by adding an acid thereto, activating a powderedcomposition (or other dry composition) by adding water thereto, orpreparing an activated dry composition which releases chlorine dioxideover time. U.S. Pat. No. 4,547,381 (issued Oct. 15, 1985) and U.S. Pat.No. 4,689,169 (issued Aug. 25, 1987) mention these three techniques forproducing chlorine dioxide, and disclose in some detail one type of suchan activated dry composition. They teach that this activated drycomposition is a mixture of a “dry inert diluent,” a metal chlorite, anda dry agent capable of reacting with the metal chlorite in a dry stateto produce chlorine dioxide. The metal chlorite can be sodium chlorite,and the dry agent can be a “dry acid” such as granular citric acid. Theinert diluent can be diatomaceous earth, sodium chloride, sodiumsilicate, disodium sulfate, or magnesium chloride, or a combination oftwo or more thereof. The mixture releases chlorine dioxide over timeuntil the rate of chlorine dioxide release becomes low, and the patentsteach that the mixture can then be agitated for “renewed generation” ofchlorine dioxide.

[0009] However, an activated composition (such as that described in U.S.Pat. Nos. 4,547,381 and 4,689,169) is subject to undesirable storage andshipping losses, due to outgassing of chlorine dioxide before the timeof intended use of the composition.

[0010] Similarly, the inventor has found that sodiumchlorite-impregnated zeolite crystals (of the type described inreferenced U.S. Pat. Nos. 5,567,405 and 5,573,743) are also subject toundesirable storage and shipping losses, due to outgassing of chlorinedioxide therefrom before the time of their intended use (e.g., beforefluid is caused to flow through both a bed of the sodiumchlorite-impregnated zeolite crystals and a bed of acid-impregnatedzeolite crystals). Also, efforts to activate sodium chlorite-impregnatedzeolite crystals (of the type described in referenced U.S. Pat. Nos.5,567,405 and 5,573,743) with acid at low temperature (below 40 degreesFahrenheit) may fail in the sense that they will not result in releaseof sufficient amounts of chlorine dioxide.

[0011] There are also disadvantages to use of conventional metalchlorite solutions (of the type mentioned in U.S. Pat. Nos. 4,547,381and 4,689,169) to produce chlorine dioxide. For example, when such aconventional solution is activated (by adding an acid thereto) torelease chlorine dioxide gas, it is difficult or impossible to controlthe rate of release of the chlorine dioxide gas. Overproduction ofchlorine dioxide often results.

[0012] There are also disadvantages to use of conventional powdered ordry compositions of the type activated by adding water thereto torelease chlorine dioxide (as mentioned, for example, in U.S. Pat. Nos.4,547,381 and 4,689,169). Masschelein, in the book ChlorineDioxide—Chemistry and Environmental Impact of Oxychlorine Compounds(published 1979 by Ann Arbor Science Publishers Inc., Ann Arbor, Mich.)at page 140, describes one such dry mixture comprising sodium chlorite,and a solid organic anhydride containing 2 to 20% of a desiccatingproduct such as calcium chloride. When such a conventional drycomposition is activated (by adding water thereto) to release chlorinedioxide gas, it is typically difficult or impossible to control the rateof release of the chlorine dioxide to achieve chlorine dioxide releaserates useful for such applications as air or water filtration.Overproduction of chlorine dioxide often results.

[0013] Until the present invention, it was not known how to produce astable, unactivated substance (either in liquid or dry form) which doesnot release significant amounts of chlorine dioxide until activated byexposure to an acid, and which releases chlorine dioxide at a useful(and controllable) rate when exposed to an acid (even at temperaturesbelow 40 degrees Fahrenheit). Nor had it been known to use such astable, unactivated substance to produce controlled release of chlorinedioxide for filtering air or water.

SUMMARY OF THE INVENTION

[0014] In some embodiments, the invention is a method for producingchlorine dioxide by activating zeolite crystals (previously impregnatedwith sodium chlorite and calcium chloride) with excess protons oractivating an aqueous solution of sodium chlorite and calcium chloridewith excess protons. Typically, the excess protons are produced byexposing the crystals to an acid (or other proton generating species),or exposing the aqueous solution of sodium chlorite and calcium chlorideto an acid (or other proton generating species). Examples of protongenerating species useful for such activation are acids such as aceticacid, phosphoric acid, citric acid, HCl, propionic acid, and sulfuricacid, and metal salts such as ferric chloride, ferric sulfate, ZnSO₄,ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, and MgSO₄. In someembodiments the proton generating species releases excess protons uponexposure to the impregnated zeolite crystals themselves. In otherembodiments the proton generating species must itself be activated tocause it release excess protons, so that the protons can in turnactivate the impregnated zeolite crystals.

[0015] In accordance with the invention, the step of activating zeolitecrystals with excess protons can be performed by causing a fluid (e.g.,air, another oxygen-containing fluid, or water) to flow through a bed ofzeolite crystals impregnated with sodium chlorite and calcium chloride,and a bed of zeolite crystals impregnated with the proton generatingspecies. The two beds can be physically mixed together, or the fluid canbe caused to flow sequentially through distinct first and second beds(preferably first through the bed containing proton generatingspecies-impregnated zeolite, but alternatively first through the bedcontaining sodium chlorite and calcium chloride-impregnated zeolite).Alternatively, chlorine dioxide is produced using sodium chlorite andcalcium chloride-impregnated zeolite crystals by immersing theimpregnated zeolite in (or spraying the impregnated zeolite with) acidor another proton generating species, or otherwise exposing theimpregnated zeolite to acid (preferably aqueous acetic, phosphoric,citric acid, HCl, sulfuric acid, propionic acid, or another acid, with aconcentration of 0.025% to 0.5%, in the sense that the acid comprises0.025% to 0.5% by weight of the combined impregnated zeolite and acid)or another proton generating species.

[0016] To produce chlorine dioxide using the inventive aqueous solutionof sodium chlorite and calcium chloride, the solution can be mixed (orotherwise combined) with acid. The liquid mixture can then be sprayed orcoated on a surface (or the liquid mixture can be absorbed in a materialsuch as a sponge, pad, mat, or the like, or simply placed in areservoir, container, box, or the like) from which chlorine dioxide gascan escape at a desired rate.

[0017] In any of the embodiments, the rate of chlorine dioxide release(following activation) can be controlled in any of several ways,including by appropriately selecting the concentration and amount of theactivating acid (or other proton generating species), and usingimpregnated zeolite having appropriately selected weight ratios of metalchlorite (e.g., sodium chlorite) or sodium chlorate to zeolite, anddeliquescent or water absorbing and retaining substance (e.g., calciumchloride) to zeolite.

[0018] Other embodiments of the invention are substances useful forproducing chlorine dioxide, which are stable until activated with excessprotons (in the sense that they do not release chlorine dioxide gas insignificant amounts until so activated with protons). One suchembodiment is one or more zeolite crystals impregnated with sodiumchlorite and calcium chloride. Preferably, the zeolite crystals aresmall (each of size in a range from 0.2 mm to one quarter inch). Alsopreferably, the crystals comprise 1%-6% sodium chlorite, 0.5%-2% calciumchloride, 0%-20% (4%-8% in some preferred embodiments) water, and72%-98.5% (8%-94.5% in some preferred embodiments) zeolite by weight.Another such embodiment is an aqueous solution of sodium chlorite and atleast one chemical selected from the group consisting of magnesiumsulfate, potassium chloride, potassium hydroxide, and calcium chloride,preferably comprising 1%-6% of sodium chlorite, 0.5%-2% of said at leastone chemical, and 92%-98.5% of water (by weight). Preferably, thesolution comprises 1%-6% sodium chlorite, 0.5%-2% calcium chloride, and92%-98.5% water (by weight).

[0019] In variations on any embodiment of the invention, awater-retaining substance other than calcium chloride, such as magnesiumsulfate (MgSO₄), potassium chloride, or potassium hydroxide, issubstituted for calcium chloride. For example, zeolite crystalsimpregnated with sodium chlorite and magnesium sulfate are within thescope of the invention. For another example, a method of producingchlorine dioxide by activating an aqueous solution of sodium chloriteand magnesium sulfate with an acid is also within the scope of theinvention.

[0020] In other variations on any embodiment of the invention, a metalchlorite other than sodium chlorite is substituted for sodium chlorite.For example, zeolite crystals impregnated with calcium chloride (ormagnesium sulfate) and a metal chlorite other than sodium chlorite arewithin the scope of the invention.

[0021] The inventor has found that the presence (in a sufficient amount)of calcium chloride (or another water-retaining substance such asmagnesium sulfate, potassium chloride, or potassium hydroxide) in theunactivated composition of the invention reduces the rate of chlorinedioxide outgassing to no more than a negligible amount at times prior toactivation of the composition with protons, and yet allows release ofchlorine dioxide at a desired rate following activation of thecomposition with protons. One of the reasons for chlorine dioxideoutgassing (prior to activation with excess protons) from zeoliteimpregnated with metal chlorite (but not impregnated with awater-retaining substance such as calcium chloride) is migration ofprotons in the aluminosilicates comprising the zeolite.

[0022] In other embodiments, the invention is a method for producingchlorine dioxide, including the steps of providing a zeolite crystalmixture, wherein the mixture comprises zeolite crystals impregnated withsodium chlorate and zeolite crystals impregnated with an oxidizer, andactivating the mixture with excess protons, and a zeolite crystalmixture for use in performing such method. In other embodiments, theinvention is a method for producing chlorine dioxide, including thesteps of providing a zeolite crystal mixture, wherein the mixturecomprises zeolite crystals impregnated with a proton generating speciesand zeolite crystals impregnated with an oxidizer (or sodium chlorate),and causing the zeolite crystal mixture to come in contact with sodiumchlorate solution (or an oxidizer, where the mixture includes zeolitecrystals impregnated with sodium chlorate but not an oxidizer), and azeolite crystal mixture for use in performing such method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross-sectional view of a zeolite crystal impregnatedwith a metal chlorite, and one of calcium chloride (or otherdeliquescent or water absorbing and retaining substance), magnesiumsulfate, potassium chloride, and potassium hydroxide.

[0024]FIG. 2 is a cross-sectional view of a zeolite crystal impregnatedwith a proton generating species, or another substance or mixture ofsubstances in accordance with any of the embodiments of the invention.

[0025]FIG. 3 is a cross-sectional view of a mixture of impregnatedzeolite crystals (prepared in accordance with any embodiment of theinvention) in a sealed container.

[0026]FIG. 4 is a cross-sectional view of a mixture of impregnatedzeolite crystals (prepared in accordance with the invention) surroundedby a barrier permeable to chlorine dioxide gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In one class of embodiments, the invention is a process forimpregnating zeolite crystals with sodium chlorite and calcium chloride,and the product of such process. The zeolite crystals can have size(i.e., largest dimension) equal (or approximately equal) to 0.125 inch,0.25 inch, 0.50 inch, or 0.75 inch, or size in the range from 0.2 mm toseveral millimeters, or size in the range from 0.2 mm to 0.25 inch, orthe zeolite crystals can have dimensions equal or substantially equal to0.25 inch×0.167 inch, 0.125 inch×0.10 inch, 0.25 inch×0.125 inch, 0.125inch×0.50 inch, or 0.50 inch×0.75 inch. The impregnation processproduces zeolite crystals uniformly impregnated (throughout the volumeof each crystal) with sodium chlorite and calcium chloride.

[0028] Preferred embodiments of this impregnation process employ, asinput material, zeolite crystals whose moisture content has been reduced(substantially below an initial moisture content) to a low level(preferably about 5%). Such input material is preferably produced bymining zeolite, crushing the mined mineral into appropriately sizedzeolite crystals (having a natural moisture content substantially above5%, and then dehydrating the zeolite crystals until their moisturecontent is reduced to about 5%.

[0029] The dehydrated zeolite crystals are then immersed in (or sprayedwith) an aqueous solution of sodium chlorite and calcium chloride athigh temperature (e.g., in the range from 120° F. to 190° F.), and theresulting slurry is thoroughly mixed. Then, the mixed slurry is airdried (or allowed to equilibrate) to the desired moisture level(typically 0-20%) to produce impregnated zeolite crystals.Alternatively, the air drying step can be avoided by calculating theamount of aqueous impregnating material needed to achieve the desiredfinal moisture level (e.g., 15%) and adding this amount to thedehydrated zeolite at the time of impregnation.

[0030] Alternatively, the dehydrated zeolite crystals are immersed in(or sprayed with) an aqueous solution of sodium chlorite at hightemperature (e.g., at least 190°F.), and the resulting slurry isthoroughly mixed. Then, the mixed slurry is air dried (or allowed toequilibrate) to the desired moisture level to produce sodiumchlorite-impregnated zeolite crystals. Alternatively, one calculates theamount of aqueous sodium chlorite needed to achieve the desired moisturelevel (e.g., a desired level in the range 15%-20%) and adds this amountto the dehydrated zeolite at the time of impregnation. Then, the sodiumchlorite-impregnated zeolite crystals are immersed in (or sprayed with)an aqueous solution of calcium chloride at high temperature, and theresulting slurry is thoroughly mixed. Then, the mixed slurry is airdried (or allowed to equilibrate) to the desired final moisture level(typically 0-20%) to produce zeolite crystals impregnated with bothsodium chlorite and calcium chloride. Alternatively, air drying isavoided by calculating the amount of aqueous calcium chloride needed toachieve the desired final moisture level (e.g., a desired level in therange 15%-20%) and adding this amount to the sodium chlorite-impregnatedzeolite at the time of calcium chloride impregnation.

[0031] In variations of any of the described zeolite impregnationprocesses, a water-retaining substance such as magnesium sulfate(MgSO₄), potassium chloride, or potassium hydroxide is substituted forcalcium chloride as an impregnating agent.

[0032] In other variations on the described zeolite impregnationprocesses, a metal chlorite other than sodium chlorite is substitutedfor sodium chlorite.

[0033]FIG. 1 represents one impregnated zeolite crystal, having channelsuniformly impregnated with mixture 2 of metal chlorite and awater-retaining substance. The water-retaining substance is preferablycalcium chloride, but alternatively is magnesium sulfate, potassiumchloride, potassium hydroxide, or another water-retaining substance. Themetal chlorite is preferably sodium chlorite.

[0034] The rate at which impregnated zeolite crystals of the type shownin FIG. 1 (e.g., zeolite crystals uniformly impregnated sodium chloriteand calcium chloride) react with in the presence of excess protons torelease chlorine dioxide can be controlled (reduced or increased to adesired level) by varying the relative amounts (by weight) of thedifferent impregnating agents therein.

[0035] In some embodiments of the invention, the proton generatingspecies is in the form of zeolite crystals impregnated with one or moremetal salts (preferably one or more of ferric chloride, ferric sulfate,ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, and MgSO₄). Uponexposure of the metal salt or salts to water (either liquid water or amoisture-containing gas, e.g. atmospheric moisture), excess protons aregenerated.

[0036] In other embodiments of the invention, the proton generatingspecies is activated (other than by exposure to water) to release excessprotons. The proton generating species is activated in such a mannerthat impregnated zeolite crystals are exposed to excess protons, therebyinitiating a reaction resulting in release of chlorine dioxide gas. Insome embodiments, the proton generating species releases excess protonsupon exposure to the impregnated zeolite crystals themselves (theimpregnated zeolite crystals together with the proton generating speciesdoes not need to be further activated to cause the proton generatingspecies to release excess protons).

[0037] In some embodiments of the invention, the proton generatingspecies is in the form of zeolite crystals impregnated with at lease oneacid (preferably one or more of acetic acid, citric acid, phosphoricacid, HCl, propionic acid, and sulfuric acid). Above-referenced U.S.Pat. Nos. 5,567,405 and 5,573,743 disclose methods for producing suchacid-impregnated zeolite crystals. Briefly, the acid impregnation stepis preferably performed by immersing dehydrated zeolite crystals in (orspraying zeolite crystals with) an aqueous solution of one or more ofthe acids at high temperature, thoroughly mixing the resulting slurry,and finally air drying (or allowing the slurry to equilibrate) to thedesired moisture level (e.g. 0%-20%) the mixed slurry to produce theacid-impregnated zeolite crystals. FIG. 2 represents one suchimpregnated crystal, having channels uniformly impregnated (throughoutthe volume of the crystal) with chemical 10, where chemical 10 is aceticacid, citric acid, phosphoric acid, HCl, propionic acid, or sulfuricacid (or another acid), or a mixture of two or more of such acids, oranother proton generating species, or another substance or mixture ofsubstances in accordance with any of the embodiments of the invention.

[0038] In general, the acid or acids employed (for activation ofimpregnated zeolite crystals) in accordance with the invention can beimpregnated in zeolite crystals, mixed in an aqueous solution (includinga metal chlorite and a water-retaining substance such as calciumchloride), or added to (e.g., sprayed on) zeolite crystals that havebeen impregnated with a metal chlorite and a water-retaining substancesuch as calcium chloride.

[0039] With reference again to zeolite crystals that have beenimpregnated in accordance with the invention with sodium chlorite andcalcium chloride, such crystals are preferably small (each of size in arange from 0.2 mm to one quarter inch), and each crystal preferablycomprises 1%-6% sodium chlorite, 0.5%-2% calcium chloride, 0%-20% (4%-8%in some preferred embodiments) water, and 72%-98.5% (84%-94.5% in somepreferred embodiments) zeolite by weight. The inventor has foundthat-the presence of calcium chloride (preferably in the preferredamount noted above) in the unactivated impregnated zeolite reduces therate of chlorine dioxide outgassing to no more than a negligible amountuntil activation of the composition with acid, and yet allows release ofchlorine dioxide at a desired rate following activation of thecomposition with acid. This finding was unexpected, since mixing ofsodium chlorite and calcium chloride with water would have been expectedto produce chlorine dioxide as a result of the following sequence ofreactions:

[0040] 1. 2NaClO₂+2H₂O+CaCl₂→

[0041] 2. Ca(OH)₂+2HCL+2NaClO₂→

[0042] 3. HCL+NaClO₂+NaCl+ClO₂↑+protons.

[0043] Instead, the unexpected finding that the rate of chlorine dioxideoutgassing is substantially reduced is believed to result from thefollowing reaction:

[0044] 1. 2NaClO₂+H₂O+CaCl₂→

[0045] 2. H₂O+CaClO₂+2NaCl.

[0046] The products of this reaction, when activated with excess protons(e.g., by exposure to acid or a metal salt) are converted to C10 ₂↑ andother substances including excess protons. In another embodiment, whensodium chlorite and ferric chloride react with water to produce chlorinedioxide gas, it is believed that the chlorine dioxide is produced as aresult of the following reaction: 3NaClO₂+3H₂O+FeCl₃→3ClO₂+(Fe)(OH)₃+3NaCl.

[0047] In another class of embodiments, the invention is an aqueoussolution of sodium chlorite and calcium chloride (or sodium chlorite anda water-retaining substance other than calcium chloride). This solutioncan be activated by exposure to protons (e.g., as a result of exposureto a proton generating species such as acetic acid, phosphoric acid,citric acid, or another acid) so as to release chlorine dioxide in acontrolled manner. Preferably, the solution comprises 1%-6% sodiumchlorite, 0.5%-2% calcium chloride, and 92%-98.5% water (by weight).Also preferably, the solution is activated by being mixed (or otherwisecombined) with aqueous acetic acid, phosphoric acid, citric acid, HCl,propionic acid, or sulfuric acid (or another acid) having aconcentration of 0.025% to 0.5% (by weight of the total mixture). Anexample of such an aqueous acid is produced by adding 1k (by weight ofthe total mixture) of a 3% aqueous acetic acid solution. The activatedliquid mixture (of aqueous sodium chlorite, calcium chloride, and acid)can then be sprayed or coated on a surface (or the liquid mixture can beabsorbed in a material such as a sponge, pad, mat, or the like, orsimply placed in a reservoir) from which chlorine dioxide gas can escapeat a desired rate.

[0048] The inventor has found that the presence of diluted calciumchloride or one of the alternative water-retaining substances(preferably in the above-noted preferred amount of 0.5%-2% by weight) inthe unactivated solution reduces the rate of chlorine dioxide outgassingto no more than a negligible amount at times prior to activation with anacid, and yet allows release of chlorine dioxide at a desired rate uponactivation of the solution with acid. The unexpected finding that therate of chlorine dioxide outgassing (prior to activation) issubstantially reduced is believed to result from the following reactionin the unactivated solution:

[0049] 1. 2NaClO₂+H₂O+CaCl₂→

[0050] 2. H₂O+CaClO₂+2NaCl. The products of this reaction, whenactivated with excess protons (e.g., by addition of acid) are convertedto ClO₂↑ and other substances including excess protons.

[0051] The impregnated zeolite crystals of the invention (crystalsimpregnated with a metal chlorite and calcium chloride, or a metalchlorite and a water-retaining substance other than calcium chloride)are useful in a class of methods for producing chlorine dioxide (ClO₂).Such methods will be described in preferred embodiments in which calciumchloride is an impregnating agent and the metal chlorite is sodiumchlorite, but it should be understood that a water-retaining substance(such as magnesium sulfate, potassium chloride, or potassium hydroxide)can be substituted for calcium chloride as an impregnating agent in themethods (and that a metal chlorite other than sodium chlorite can besubstituted for sodium chlorite).

[0052] In one chlorine dioxide-producing method in accordance with theinvention, a fluid (preferably a fluid containing oxygen, such as air orwater) is caused to move relative to a first bed (i.e., the fluid flowsthrough the first bed or the crystals comprising the first bed movethrough the fluid) of zeolite crystals impregnated with: (1) phosphoricacid (H₃PO₄), (2) acetic acid (CH₃COOH), (3) citric acid, (4) ferricchloride (FeCl₃), (5) ferric sulfate, or (6) another metal salt, such asZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, or MgSO₄, or (7)an acid other than phosphoric, acetic, or citric acid, or another protongenerating species suitable for the particular application. Then, thefluid is caused to move relative to a second bed (i.e., the fluid flowsthrough the second bed, or the crystals comprising the second bed movethrough the fluid) of zeolite crystals which are impregnated with amixture of sodium chlorite (NaClO₂) and calcium chloride (CaCl₂). Uponmoving the fluid relative to the second bed, chlorine dioxide isreleased (due to contact with acid or other proton generating substancetransferred from the first bed). It is believed that the chlorinedioxide release occurs as a result of the following reaction, in thecase of a first bed impregnated with acetic acid:

CH₃COOH+CaClO₂+2NaCl+H₂O→ClO₂↑+Ca(CH₃COO)₂+excess protons,

[0053] where Ca(CH₃COO)₂ is calcium acetate.

[0054] As discussed above, CaClO₂, 2NaCl, and H₂O are believed to bepresent in the channels of the zeolite crystals of the first bed as aresult of reaction of the impregnating agents NaClO₂ and CaCl₂, and H₂O,in the channels of the zeolite crystals of the first bed.

[0055] In variations on this chlorine dioxide production method, thefirst bed can include a mixture of phosphoric acid-impregnated zeolitecrystals and acetic acid-impregnated zeolite crystals, or a mixture ofphosphoric acid-impregnated zeolite crystals and citric acid-impregnatedzeolite crystals, or a mixture of acetic acid-impregnated zeolitecrystals and citric acid-impregnated zeolite crystals, or a mixture ofall three types of acid-impregnated zeolite crystals, or a mixture ofzeolite crystals impregnated with one of these three types of acids andzeolite crystals impregnated with another acid (e.g., HCl or H₂SO₄).

[0056] It is preferable for the fluid to flow through a first bed ofproton generating species-impregnated (e.g., acid-impregnated) zeolitecrystals before the fluid flows through a second bed containing sodiumchlorite and calcium chloride-impregnated zeolite crystals, since thissequence will result in protons entering the fluid (due to interactionof the fluid with the acid or other proton generating species in thecrystals of the first bed), and since the presence of the hydrogen ionsin the fluid will enhance chlorine dioxide production when the hydrogenion-containing fluid interacts with the impregnating chemical in thecrystals of the second bed.

[0057] While the foregoing process for producing ClO₂ has been describedwith reference to two distinct (first and second) beds of impregnatedzeolite crystals, a single bed containing a mixture of crystals can beused as long as the mixed bed contains both impregnated zeolite crystalsfrom the first bed described above and zeolite crystals from the secondbed described above. As an example, a mixed bed of zeolite crystals(zeolite crystals impregnated with sodium chlorite and calcium chloridemixed with zeolite crystals impregnated with phosphoric acid) can beused to produce chlorine dioxide (e.g., by flowing a fluid through themixed bed).

[0058] Alternatively, chlorine dioxide can be produced by adding aqueousacid to a bed of zeolite crystals impregnated with a metal chlorite(e.g., sodium chlorite) and a water-retaining substance (e.g., calciumchloride). In these alternative embodiments, the rate of release ofchlorine dioxide can be controlled by varying the amount andconcentration of the added acid.

[0059] In alternative embodiments, chlorine dioxide is produced with areversed sequence of distinct first and second beds, as follows. A fluid(preferably a fluid containing oxygen such as air) is caused to moverelative to a first bed (i.e., the fluid flows through the first bed, orthe crystals comprising the first bed move through the fluid). The firstbed comprises zeolite crystals impregnated with sodium chlorite (NaClO₂)and calcium chloride (CaCl₂). Then, the fluid is caused to move relativeto a second bed (i.e., the fluid flows through the second bed, or thecrystals comprising the second bed move through the fluid) of zeolitecrystals which are impregnated with: (1) phosphoric acid, (2) aceticacid, (3) citric acid, (4) ferric chloride (FeCl₃), (5) ferric sulfate,or (6) another metal salt, such as ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄,MnCl₂, CuSO₄, CuCl₂, or MgSO₄, or (7) an acid other than phosphoric,acetic, or citric acid, or another proton generating species suitablefor the particular application. Upon moving the fluid relative to thesecond bed, chlorine dioxide is released. As with other embodimentsdescribed herein, a water-retaining substance such as magnesium sulfate,potassium chloride, or potassium hydroxide can be substituted for thecalcium chloride (and a metal chlorite other than sodium chlorite can besubstituted for the sodium chlorite).

[0060] In another class of embodiments of the inventive chlorine dioxideproduction method, zeolite crystals impregnated with sodium chlorite andcalcium chloride are activated by being immersed in (or sprayed with)aqueous acetic acid, phosphoric acid, citric acid, HCl, or sulfuricacid, with a concentration of 0.025% to 0.5% (in the sense that the acidcomprises 0.025% to 0.5% by weight of the combined impregnated zeoliteand acid). Alternatively, another acid or other proton generatingspecies suitable for the particular application can be used to immerse(or spray) the impregnated zeolite crystals as a substitute for theaqueous acetic acid, phosphoric acid, citric acid, HCl, or sulfuricacid.

[0061] While chlorine dioxide can kill microorganisms in the fluidundergoing treatment, and can oxidize volatile organic chemicals whichcontaminate the fluid undergoing treatment (as described above),chlorine dioxide itself is a contaminant. Therefore, it is sometimesdesirable to remove chlorine dioxide from the fluid stream after thechlorine dioxide has performed purification (including biologicalpurification) of the fluid stream. Another aspect of the presentinvention relates to a multi-step filtration process in which chlorinedioxide is first produced in a fluid stream and, subsequently, removedfrom the fluid stream.

[0062] First, a fluid is caused to be moved relative to a primary bed(or primary beds) of zeolite crystals (i.e., the described first andsecond beds, or the described mixed bed) which will cause chlorinedioxide to be released, as described above. While the fluid movesrelative to (e.g., while the fluid flows through) the primary bed orbeds, chlorine dioxide is released (generally as a gas). The releasedchlorine dioxide will kill biological contaminants in the fluid and willoxidize volatile organic chemicals which contaminate the fluid.

[0063] Then, the fluid is moved relative to a secondary bed (filter) ofzeolite crystals impregnated with one of the following: (1) potassiumhydroxide (KOH), (2) sodium sulfite, (3) sodium bisulfite, and (4)ferrous sulfate (i.e., the fluid flows through the secondary bed or thecrystals comprising the secondary bed move through the fluid). Thezeolite crystals of the secondary bed react with the chlorine dioxide toremove the chlorine dioxide from the fluid. Some chemical equationsdescribing possible reactions in the secondary bed follow.

[0064] For a secondary bed of potassium hydroxide:

2KOH+2ClO₂→KClO₂+KCLO₄+H₂O

[0065] For a secondary bed of sodium sulfite:

ClO₂+Na₂SO₃→H₂O+S₂O₅+H⁺ ₃ClO₃

[0066] Note that H⁺⁺ from the acids involved in the previous reactionscancel this reaction.

[0067] For a secondary bed of sodium bisulfite:

ClO₂+Na₂SO₅→H₂O+S₂O₅+H⁺ ₃ClO₃

[0068] Note that H⁺⁺ from the acids involved in the previous reactionscancel this reaction.

[0069] The preferred composition of the secondary bed is ferroussulfate. For a secondary bed of ferrous sulfate:

ClO₂+Fe⁺⁺SO₄→Fe⁺⁺⁺+Cl⁻+ClO₂ ⁻→FeCl₃ (primarily).

[0070] When using a secondary bed of ferrous sulfate a color change,from white to brown, takes place. This is an indicator ofneutralization.

[0071] Various modifications and variations of the described methods andcompositions of the invention will be apparent to those skilled in theart without departing from the scope and spirit of the invention. Forexample, a carrier other than zeolite crystals or water (e.g., pumice,diatomaceous earth, bentonite, or clay) can be used to carry the metalchlorite and water-retaining substance (and optionally also the acid orother proton generating species) of the invention.

[0072] We next describe other classes of embodiments of the invention.

[0073] In one such class of embodiments, the invention is a method forproducing chlorine dioxide by activating a mixture comprising zeolitecrystals impregnated with sulfuric acid (or other proton generatingspecies), zeolite crystals impregnated with sodium chlorate, zeolitecrystals impregnated with an oxidizer, and optionally also zeolitecrystals impregnated with calcium chloride (or another deliquescent orwater absorbing and retaining substance). The oxidizer is a substance(or mixture of substances) which reacts (in the presence of waterabsorbed by the deliquescent or water absorbing substance) to releaseanother substance which in turn reacts with one or more of the otherimpregnating substances to produce chlorine dioxide. In some of theseembodiments, the oxidizer is ferric chloride or ferric sulfate, or amixture of ferric chloride and ferric sulfate. Although each of theseiron salts desirably absorbs water in addition to functioning as anoxidizer, ferric chloride is preferably used (rather than ferricsulfate, or a mixture of ferric chloride and ferric sulfate) since it isthe most reactive during performance of the inventive method. Wheresodium chlorate, ferric chloride, and sulfuric acid are present uponactivation, the chlorine dioxide-producing reaction is believed to be:2Na(ClO₃)+FeCl₃+H₂SO₄+3H₂O→Na₂SO₄+Fe(OH)₃+3HCl+2H₂O+2ClO₂↑. In any ofthis class of embodiments, the activation can be accomplished byexposing the mixture to a moisture-containing gas (e.g., air includingwater vapor), or (to achieve a higher chlorine dioxide production rate)causing water or a moisture-containing gas to flow through the mixture(or by causing the mixture to move through the gas). When activation isaccomplished using a flowing fluid, all the impregnated zeolite crystalscan be physically mixed together in a single bed, or the gas can becaused to flow sequentially through distinct beds of subsets of thezeolite crystals.

[0074] In other embodiments, chlorine dioxide is produced by activating(with excess protons) a zeolite crystal mixture comprising zeolitecrystals impregnated with sodium chlorate, zeolite crystals impregnatedwith at least one oxidizer (e.g., hydrogen peroxide, ferric chloride, orperacetic acid), and optionally also zeolite crystals impregnated withcalcium chloride. Preferably, the mixture comprises equal (orsubstantially equal) amounts of crystals impregnated with each of thefour species. The activation can be accomplished by exposing the mixtureto a moisture-containing gas (e.g., air including water vapor), or (toincrease the chlorine dioxide production rate) causing water or amoisture-containing gas (e.g., air including water vapor) to flowthrough the mixture. When activation is accomplished using flowingfluid, all impregnated zeolite crystals can be physically mixed togetherin a single bed, or the fluid can be caused to flow sequentially throughdistinct beds of subsets of the zeolite crystals. In embodiments inwhich the impregnated crystal mixture comprises distinct beds ofdifferent subsets of zeolite crystals (e.g., a bed of crystalsimpregnated with a first substance, and another bed of crystalsimpregnated with a second substance mixed with crystals impregnated witha third substance), the fluid must flow sequentially through the beds toaccomplish activation.

[0075] Where sodium chlorate, hydrogen peroxide, and sulfuric acid arepresent upon activation, the chlorine dioxide-producing reaction isbelieved to be 2Na(ClO₃)+H₂O₂+H₂SO₄→2ClO₂↑+Na₂SO₄+H₂O.

[0076] In variations on the embodiments described in the previousparagraph, zeolite crystals impregnated with sodium metabisulfite (orsodium bisulfite) are used rather than zeolite crystals impregnated withat least one of hydrogen peroxide, ferric chloride, and peracetid acid.Activation of the mixture by absorbed water (water absorbed by thedeliquescent or water absorbing and retaining substance) causes areaction of the sodium metabisulfite (or sodium bisulfite) whichreleases sulfur dioxide (SO₂). The SO₂ then reacts to form chlorinedioxide gas. Each of sodium metabisulfite and sodium bisulfite isconsidered an “oxidizer” in the sense that the latter expression is usedherein, since each reacts (in the presence of the absorbed water) torelease sulfur dioxide which in turn reacts with one or more of theother impregnating substances to produce chlorine dioxide.

[0077] In other embodiments, chlorine dioxide is produced by activatinga zeolite crystal mixture comprising zeolite crystals impregnated withsodium chlorate, zeolite crystals impregnated with sulfuric acid (oranother proton generating species, such as ferric chloride, ferricsulfate, ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, andMgSO₄ or another metal salt), zeolite crystals impregnated with anoxidizer, and optionally also zeolite crystals impregnated with adeliquescent (or water absorbing and retaining substance). As in otherembodiments, activation of the zeolite crystal mixture can beaccomplished by exposing the mixture to a moisture-containing gas (e.g.,air including water vapor), or (in order to increase the chlorinedioxide production rate) by causing water or a moisture-containing gasto flow through the mixture (or causing the mixture to move through suchfluid). When activation is accomplished using flowing fluid, theimpregnated zeolite crystals can be physically mixed together in asingle bed or the fluid can be caused to flow sequentially throughdistinct beds of subsets of the zeolite crystals. In some of theseembodiments, the deliquescent (or water absorbing and retainingsubstance) is magnesium sulfate (MgSO₄), potassium chloride, ormagnesium chloride (MgCl).

[0078] In other embodiments, the invention is a method for producingchlorine dioxide by activating an impregnated zeolite crystal mixturewith an oxidizer (such as ferric chloride solution (preferably) orliquid hydrogen peroxide or liquid peracetic acid). The zeolite crystalmixture comprises zeolite crystals impregnated with sodium chlorate,zeolite crystals impregnated with sulfuric acid (or another protongenerating species), and optionally also zeolite crystals impregnatedwith calcium chloride (or another deliquescent or water absorbing andretaining substance).

[0079] In other embodiments, the invention is a method for producingchlorine dioxide by activating an impregnated zeolite crystal mixturewith excess protons, such as by exposing it to liquid sulfuric acid (oranother proton generating species). The zeolite mixture compriseszeolite crystals impregnated with sodium chlorate, zeolite crystalsimpregnated with an oxidizer (e.g., at least one of hydrogen peroxide,ferric chloride, and peracetic acid), and optionally also zeolitecrystals impregnated with calcium chloride (or another deliquescent orwater absorbing and retaining substance).

[0080] In other embodiments, the invention is a method for producingchlorine dioxide by activating an impregnated zeolite crystal mixturewith sodium chlorate solution. The zeolite mixture comprises zeolitecrystals impregnated with sulfuric acid (or another proton generatingspecies), zeolite crystals impregnated with an oxidizer (e.g., at leastone of hydrogen peroxide, ferric chloride, and peracetic acid), andoptionally also zeolite crystals impregnated with calcium chloride (oranother deliquescent or water absorbing and retaining substance).

[0081] Also within the scope of the invention are methods in whichmixtures of two or more of the above-described impregnated zeolitemixtures are activated to produce chlorine dioxide. An example is amethod for producing chlorine dioxide by activating a zeolite crystalmixture comprising zeolite crystals impregnated with sulfuric acid,zeolite crystals impregnated with sodium chlorate, zeolite crystalsimpregnated with at least one of hydrogen peroxide, ferric chloride, andperacetic acid, zeolite crystals impregnated with calcium chloride, andzeolite crystals impregnated with sodium metabisulfite (or sodiumbisulfite).

[0082] In any embodiment of the invention, the rate of chlorine dioxiderelease (upon activation of the zeolite crystal mixture) can becontrolled in any of several ways, including by appropriately selectingthe concentration and amount of an activating liquid (e.g., where theactivating liquid is sodium chlorate solution or liquid sulfuric acid),using impregnated zeolite crystals having an appropriately selectedweight ratio of one or more of the impregnating substances (e.g., ironsalt) to zeolite, and selecting an appropriate method for activating themixture. For example, activation by exposing the mixture tomoisture-containing gas typically results in a low chlorine dioxiderelease rate, and activation by flowing water or moisture-containing gasthrough the mixture typically results in a higher chlorine dioxiderelease rate. Prior to activation, the mixture of impregnated crystalsshould be as dry as possible. Preferably, the mixture (e.g., mixture ofimpregnated zeolite crystals 40 of FIG. 3) is sealed within a dry,air-tight capsule or other container (e.g., container 41 of FIG. 3), andthe container is unsealed to expose the mixture to the activating fluidshortly before activation.

[0083] In yet another class of embodiments, the invention is a mixtureof impregnated zeolite crystals which can be activated (by any of theabove-described liquids or by water or moisture-containing gas inaccordance with the invention) to perform any embodiment of theinventive chlorine dioxide production method.

[0084] The chlorine dioxide produced in accordance with the inventioncan be used to kill microorganisms in the moisture-containing gas whichactivates the crystal mixture, and can oxidize volatile organicchemicals which contaminate the moisture-containing gas.

[0085] In another class of embodiments, the invention is composition ofmatter which carries sufficient amounts of chemicals to be capable ofreleasing chlorine dioxide to a target region upon activation by excessprotons, said composition of matter comprising a quantity of impregnatedzeolite crystals including zeolite crystals impregnated with a metalchlorite and zeolite crystals impregnated with a proton generatingspecies, wherein the quantity is capable of being activated by excessprotons to produce chlorine dioxide. Zeolite crystals 30 of FIG. 4 aresuch a quantity of impregnated zeolite crystals. Preferably, those ofcrystals 30 which are impregnated with a metal chlorite are alsoimpregnated with at least one of a deliquescent and a water absorbingand retaining substance (e.g., they are impregnated with calciumchloride) in a concentration which limits (to a predetermined maximumlevel) the rate of release of chlorine dioxide to the target region inresponse to activation of the quantity of crystals with excess protons.For example, zeolite crystals 30 can include zeolite crystalsimpregnated with metal chlorite, a water absorbing and retainingsubstance, and an acid (or other proton generating species). Suchcrystals will be activated by liquid water or atmospheric moisture(which will cause production of excess protons, which in turn will causechlorine dioxide production). The relative concentrations ofimpregnating chemicals will control the rate at which excess protons areproduced (and thus the rate at which chlorine dioxide is produced) inresponse to a specific amount of water.

[0086] For some applications, the quantity of crystals is separated by abarrier (e.g., barrier 50 of FIG. 4) from the target region. The barriershould be permeable to flow of an activating fluid (e.g., water) fromthe target region such that the activating fluid will interact with thequantity of impregnated zeolite crystals in a manner resulting inproduction of excess protons (which in turn results in production ofchlorine dioxide). The barrier should also be permeable to flow of thechlorine dioxide to the target region. Preferably, the permeability ofthe barrier is such that the quantity of zeolite crystals is exposed tono more than predetermined maximum flow rate of the activating fluid(e.g., the barrier is permeable to flow of the activating fluid from thetarget region at up to a predetermined maximum flow rate), so that thebarrier limits to a predetermined maximum level the rate of release ofchlorine dioxide to the target region.

[0087] Although the invention has been described in connection withspecific preferred embodiments, it should be understood that theinvention as claimed should not be unduly limited to such specificembodiments.

What is claimed is:
 1. A method for producing chlorine dioxide,including the steps of: (a) providing impregnated zeolite crystals whichhave been impregnated with a metal chlorite; and (b) activating theimpregnated zeolite crystals with excess protons, thereby producing thechlorine dioxide as a result of reaction of the protons with theimpregnated zeolite crystals.
 2. The method of claim 1, wherein themetal chlorite is sodium chlorite.
 3. The method of claim 1, wherein thezeolite crystals have also been impregnated with at least oneimpregnating agent selected from the group consisting of calciumchloride, magnesium sulfate, potassium chloride, and potassiumhydroxide.
 4. The method of claim 3, wherein the zeolite crystalscomprise 1%-6% sodium chlorite, 0.5%-2% calcium chloride, 0-20% water,and 72%-98.5% zeolite by weight.
 5. The method of claim 3, wherein step(b) includes the step of: exposing the impregnated zeolite crystals toexcess protons, thereby producing the chlorine dioxide as a result ofreaction of the protons with the impregnated zeolite crystals.
 6. Themethod of claim 1, wherein step (b) includes the step of exposing theimpregnated zeolite crystals to a proton generating species, therebyproducing the excess protons and producing the chlorine dioxide as aresult of reaction of the protons with the impregnated zeolite crystals.7. The method of claim 6, wherein the proton generating species is anaqueous acid.
 8. The method of claim 1, wherein step (b) includes thestep of activating a proton generating species to produce the excessprotons.
 9. The method of claim 8, wherein step (b) includes the step ofexposing the impregnated zeolite crystals to the proton generatingspecies and then activating the proton generating species to producesaid excess protons.
 10. The method of claim 8, wherein the protongenerating species comprises a metal salt, and the step of activatingsaid proton generating species is accomplished by exposing the metalsalt to water.
 11. The method of claim 10, wherein the metal salt is amember of the group consisting of ferric chloride, ferric sulfate,ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, and MgSO₄.
 12. Amethod for producing chlorine dioxide, including the steps of: (a)causing a fluid to flow through a first set of impregnated zeolitecrystals, wherein the impregnated zeolite crystals have been impregnatedwith at least one proton generating impregnating agent; and (b) afterstep (a), causing the fluid to flow through a second set of impregnatedzeolite crystals, wherein the impregnated zeolite crystals in the secondset have been impregnated with a metal chlorite and at least oneimpregnating agent selected from the group consisting of calciumchloride, magnesium sulfate, potassium chloride, and potassiumhydroxide, wherein chlorine dioxide is produced as a result of reactionof the second set of impregnated zeolite crystals with excess protonsreleased from the at least one proton generating impregnating agent. 13.The method of claim 12, wherein the metal chlorite is sodium chlorite.14. The method of claim 12, wherein the second set of impregnatedzeolite crystals consists essentially of zeolite crystals impregnatedwith sodium chlorite and calcium chloride.
 15. The method of claim 12,wherein said at least one proton generating impregnating agent is atleast one acid.
 16. The method of claim 12, wherein the fluid includeswater and said at least one proton generating impregnating agentincludes a metal salt.
 17. The method of claim 16, wherein the metalsalt is a member of the group consisting of ferric chloride, ferricsulfate, ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, andMgSO₄.
 18. A method for filtering a fluid containing a contaminant,including the steps of: (a) moving the fluid through a first bed ofimpregnated zeolite crystals which have been impregnated with one of atleast one proton generating impregnating agent and a metal chlorite; and(b) after step (a), moving the fluid through a second bed of impregnatedzeolite crystals which have been impregnated with another one of theleast one proton generating impregnating agent and the metal chlorite,wherein chlorine dioxide is produced as a result of chemical reaction ofsaid at least one proton generating impregnating agent.
 19. The methodof claim 18, wherein the fluid is air.
 20. The method of claim 18,wherein the fluid includes microorganisms, and wherein the chlorinedioxide produced in step (b) kills at least some of the microorganisms.21. The method of claim 18, wherein the fluid is contaminated withvolatile organic chemicals, and wherein the chlorine dioxide produced instep (b) oxidizes at least some of the volatile organic chemicals. 22.The method of claim 18, also including the step of: (c) after step (b),moving the fluid relative to a third bed of impregnated zeolitecrystals, wherein the impregnated zeolite crystals in the third bed areimpregnated with an impregnating agent selected from the groupconsisting of potassium hydroxide, sodium sulfite, sodium bisulfite, andferrous sulfate, so that at least some of the chlorine dioxide isremoved by chemical reaction with the third bed.
 23. The method of claim18, wherein said at least one proton generating impregnating agent is atleast one acid.
 24. The method of claim 18, wherein the fluid includeswater and said at least one proton generating impregnating agentincludes a metal salt.
 25. The method of claim 24, wherein the metalsalt is a member of the group consisting of ferric chloride, ferricsulfate, ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, andMgSO₄.
 26. The method of claim 18, wherein the first bed of impregnatedzeolite crystals have been impregnated with said at least one protongenerating impregnating agent and the second bed of impregnated zeolitecrystals have been impregnated with said metal chlorite and at least oneimpregnating agent selected from the group consisting of calciumchloride, magnesium sulfate, potassium chloride, and potassiumhydroxide, and wherein the chlorine dioxide is produced as a result ofchemical reaction of at least a portion of the second bed with at leastone of said at least one proton generating impregnating agent andprotons resulting from activation of said at least one proton generatingimpregnating agent.
 27. The method of claim 26, wherein the metalchlorite is sodium chlorite.
 28. The method of claim 27, wherein thesecond bed consists essentially of zeolite crystals impregnated withsodium chlorite and calcium chloride.
 29. The method of claim 26,wherein the second bed consists essentially of impregnated zeolitecrystals comprising 1%-6% sodium chlorite, 0.5%-2% calcium chloride,0%-20% water, and 72%-98.5% zeolite by weight.
 30. The method of claim18, wherein the first bed of impregnated zeolite crystals have beenimpregnated with said metal chlorite and at least one impregnating agentselected from the group consisting of calcium chloride, magnesiumsulfate, potassium chloride, and potassium hydroxide, and the second bedof impregnated zeolite crystals have been impregnated with said at leastone proton generating impregnating agent, and wherein the chlorinedioxide is produced as a result of chemical reaction of at least onesubstance released from the first bed with at least one of said at leastone proton generating impregnating agent and protons resulting fromactivation of said at least one proton generating impregnating agent.31. The method of claim 30, wherein the metal chlorite is sodiumchlorite.
 32. The method of claim 31, wherein the first bed consistsessentially of zeolite crystals impregnated with sodium chlorite andcalcium chloride.
 33. The method of claim 31, wherein the first bedconsists essentially of impregnated zeolite crystals comprising 1%-6%sodium chlorite, 0.5%-2% calcium chloride, 0%-20% water, and 72%-98.5%zeolite by weight.
 34. A method for filtering a fluid containing acontaminant, including the step of: (a) moving the fluid through a bedof impregnated zeolite crystals comprising a mixture of first zeolitecrystals and second zeolite crystals, wherein the first zeolite crystalshave been impregnated with at least one proton generating impregnatingagent, and the second zeolite crystals have been impregnated with ametal chlorite and at least one impregnating agent selected from thegroup consisting of calcium chloride, magnesium sulfate, potassiumchloride, and potassium hydroxide, whereby chlorine dioxide is producedas a result of reaction of the second zeolite crystals with excessprotons released from the at least one proton generating impregnatingagent.
 35. The method of claim 34, wherein the metal chlorite is sodiumchlorite.
 36. The method of claim 35, wherein the second zeolitecrystals consist essentially of zeolite crystals impregnated with sodiumchlorite and calcium chloride.
 37. The method of claim 34, wherein thesecond zeolite crystals consist essentially of impregnated zeolitecrystals comprising 1%-6% sodium chlorite, 0.5%-2% calcium chloride,0%-20% water, and 72%-98.5% zeolite by weight.
 38. The method of claim34, wherein the fluid is air.
 39. The method of claim 34, also includingthe step of: (b) after step (a), moving the fluid relative to a secondbed of impregnated zeolite crystals, wherein the impregnated zeolitecrystals in the second bed have been impregnated with an impregnatingagent selected from the group consisting of potassium hydroxide, sodiumsulfite, sodium bisulfite, and ferrous sulfate, so that at least some ofthe chlorine dioxide is removed by chemical reaction with the secondbed.
 40. The method of claim 34, wherein said at least one protongenerating impregnating agent is at least one acid.
 41. The method ofclaim 34, wherein the fluid includes water and said at least one protongenerating impregnating agent includes a metal salt.
 42. The method ofclaim 41, wherein the metal salt is a member of the group consisting offerric chloride, ferric sulfate, ZnSO₄, ZnCl₂, CoSO₄,CoCl₂, MnSO₄, MnC1₂, CuSO₄, CuCl₂, and MgSO₄.
 43. A method for producing chlorine dioxide,including the steps of: (a) providing an aqueous solution comprising1%-6% of sodium chlorite by weight, 0.5%-2% by weight of at least onechemical selected from the group consisting of calcium chloride,magnesium sulfate, potassium chloride, and potassium hydroxide, and92%-98.5% of water by weight; and (b) combining the aqueous solutionwith a proton generating species thereby producing excess protons, andthereby producing said chlorine dioxide as a result of chemical reactionof the protons with the aqueous solution.
 44. The method of claim 43,wherein the proton generating species comprises an aqueous acid.
 45. Themethod of claim 43, wherein the proton generating species comprises atleast one metal salt.
 46. The method of claim 45, wherein the at leastone metal salt is a member of the group consisting of ferric chloride,ferric sulfate, ZnSO₄, ZnCl₂, CoSO₄, CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂,and MgSO₄.
 47. The method of claim 43, wherein the at least one chemicalis calcium chloride.
 48. A composition of matter, carrying sufficientamounts of chemicals to be capable of releasing chlorine dioxide uponactivation by excess protons, said composition of matter comprising: acarrier; a metal chlorite carried by the carrier; and at least one agentcarried by the carrier, said at least one agent having been selectedfrom the group consisting of calcium chloride, magnesium sulfate,potassium chloride, and potassium hydroxide.
 49. The composition ofclaim 48, wherein the carrier has a size sufficient for filtration of afluid.
 50. The composition of claim 48, wherein the metal chlorite issodium chlorite.
 51. The composition of claim 48, wherein the agent iscalcium chloride.
 52. The composition of claim 48, wherein the carrieris a plurality of zeolite crystals, and the metal chlorite isimpregnated into at least some of the zeolite crystals.
 53. Thecomposition of claim 52, wherein the metal chlorite is sodium chlorite,and said composition comprises 1%-6% sodium chlorite by weight, 0.5%-2%calcium chloride by weight, 0%-20% water by weight, and 72%-98.5% ofsaid zeolite crystals by weight.
 54. The composition of claim 48, alsoincluding: a proton generating species carried by the carrier.
 55. Thecomposition of claim 54, wherein the proton generating species comprisesan acid.
 56. The composition of claim 54, wherein the proton generatingspecies comprises a metal salt.
 57. The composition of claim 54, whereinthe carrier is a plurality of zeolite crystals, a first subset of thezeolite crystals is impregnated with the metal chlorite, and a secondsubset of the zeolite crystals is impregnated with the proton generatingspecies.
 58. An aqueous solution, capable of releasing chlorine dioxideupon activation by acid, said solution comprising: 1%-6% sodium chloriteby weight; and 0.5%-2% by weight of at least one chemical selected fromthe group consisting of calcium chloride, magnesium sulfate, potassiumchloride, and potassium hydroxide; and 92%-98.5% water by weight. 59.The aqueous solution of claim 58, wherein said at least one chemical iscalcium chloride.
 60. The aqueous solution of claim 59, comprising:1%-6% sodium chlorite by weight; 0.5%-2% calcium chloride by weight; and92%-98.5% water by weight.
 61. A method for producing chlorine dioxide,including the steps of: (a) providing a zeolite crystal mixture whichcomprises zeolite crystals impregnated with sodium chlorate and zeolitecrystals impregnated with an oxidizer; and (b) activating the zeolitecrystal mixture with excess protons, thereby causing the zeolite crystalmixture to produce the chlorine dioxide.
 62. The method of claim 61,wherein step (b) includes the step of exposing the zeolite crystalsimpregnated with the sodium chlorate and the zeolite crystalsimpregnated with the oxidizer to a proton generating species.
 63. Themethod of claim 61, wherein the zeolite crystal mixture also compriseszeolite crystals impregnated with a proton generating species, andwherein step (b) includes the step of causing the zeolite crystalmixture to contact a moisture-containing fluid, whereby the zeolitecrystal mixture is activated to produce the chlorine dioxide.
 64. Themethod of claim 63, wherein the zeolite crystal mixture is stored in adry, air-tight container prior to step (b), and wherein step (b)includes the step of opening said container to expose the zeolitecrystal mixture to the moisture-containing fluid.
 65. The method ofclaim 63, wherein step (b) includes the step of causing themoisture-containing fluid to flow through the zeolite crystal mixture,whereby the mixture is activated by water absorbed from themoisture-containing fluid and as a result said mixture produces thechlorine dioxide.
 66. The method of claim 63, wherein the protongenerating species is sulfuric acid.
 67. The method of claim 61, whereinthe zeolite crystal mixture also includes zeolite crystals impregnatedwith at least one of a deliquescent and a water absorbing and retainingsubstance.
 68. The method of claim 61, wherein the zeolite crystalsimpregnated with said oxidizer are zeolite crystals impregnated with atleast one of hydrogen peroxide, ferric chloride, peracetic acid, sodiummetabisulfite, and sodium bisulfite.
 69. The method of claim 61, whereinthe zeolite crystal mixture, the zeolite crystal mixture also compriseszeolite crystals impregnated with calcium chloride, wherein the oxidizeris at least one of hydrogen peroxide, ferric chloride, and peraceticacid, and wherein step (b) includes the step of: causing the zeolitecrystal mixture to come in contact with liquid sulfuric acid, wherebysaid zeolite crystal mixture is activated to produce the chlorinedioxide.
 70. A method for producing chlorine dioxide, including thesteps of: (a) providing a zeolite crystal mixture, the zeolite crystalmixture comprising zeolite crystals impregnated with a proton generatingspecies and zeolite crystals impregnated with an oxidizer; and (b)causing the zeolite crystal mixture to come in contact with sodiumchlorate solution, whereby said zeolite crystal mixture is activated toproduce the chlorine dioxide.
 71. The method of claim 70, wherein thezeolite crystal mixture also comprises zeolite crystals impregnated withcalcium chloride, and wherein the proton generating species is sulfuricacid.
 72. A method for producing chlorine dioxide, including the stepsof: (a) providing a zeolite crystal mixture, the zeolite crystal mixturecomprising zeolite crystals impregnated with sodium chlorate and zeolitecrystals impregnated with a proton generating species; and (b) causingthe zeolite crystal mixture to come in contact with an oxidizer, wherebysaid zeolite crystal mixture is activated to produce the chlorinedioxide.
 73. The method of claim 72, wherein the zeolite crystal mixturealso comprises zeolite crystals impregnated with calcium chloride,wherein the proton generating species is sulfuric acid, and wherein step(b) includes the step of causing the zeolite crystal mixture to come incontact with a solution of at least one of hydrogen peroxide, ferricchloride, peracetic acid, sodium metabisulfite, and sodium bisulfite.74. A zeolite crystal mixture capable of being activated by excessprotons to produce chlorine dioxide, said mixture comprising: zeolitecrystals impregnated with sodium chlorate; and zeolite crystalsimpregnated with an oxidizer.
 75. The mixture of claim 74, wherein saidmixture also comprises zeolite crystals impregnated with at least one ofa deliquescent and a water absorbing and retaining substance.
 76. Themixture of claim 74, wherein the oxidizer is at least one of hydrogenperoxide, ferric chloride, peracetic acid, sodium metabisulfite, andsodium bisulfite.
 77. The mixture of claim 74, wherein the mixture alsocomprises: zeolite crystals impregnated with a proton generatingspecies.
 78. A zeolite crystal mixture capable of being activated by anoxidizer to produce chlorine dioxide, said mixture comprising: zeolitecrystals impregnated with sodium chlorate; and zeolite crystalsimpregnated with a proton generating species.
 79. The mixture of claim78, wherein the proton generating species is sulfuric acid, and whereinsaid mixture also comprises zeolite crystals impregnated with at leastone of a deliquescent and a water absorbing and retaining substance. 80.A composition of matter, carrying sufficient amounts of chemicals to becapable of releasing chlorine dioxide to a target region upon activationby excess protons, said composition of matter comprising: a quantity ofimpregnated zeolite crystals, wherein said quantity comprises zeolitecrystals impregnated with a metal chlorite and zeolite crystalsimpregnated with a proton generating species, and wherein said quantityis capable of being activated by excess protons to produce chlorinedioxide.
 81. The composition of matter of claim 80, also including: abarrier separating the quantity of impregnated zeolite crystals from thetarget region, wherein the barrier is permeable to flow of an activatingfluid from the target region such that the activating fluid willinteract with the quantity of impregnated zeolite crystals in a mannerresulting in production of said excess protons and production of saidchlorine dioxide, wherein the barrier is also permeable to flow of thechlorine dioxide to the target region.
 82. The composition of matter ofclaim 81, wherein the barrier is permeable to flow of the activatingfluid from the target region at up to a predetermined maximum flow rate,so that the barrier limits to a predetermined maximum level the rate ofrelease of the chlorine dioxide to the target region.
 83. Thecomposition of matter of claim 80, wherein the quantity of impregnatedzeolite crystals also comprises: zeolite crystals impregnated with atleast one of a deliquescent and a water absorbing and retainingsubstance in a concentration which limits to a predetermined maximumlevel the rate of release of the chlorine dioxide to the target region.84. The composition of matter of claim 80, wherein said zeolite crystalsimpregnated with at least one of a deliquescent and a water absorbingand retaining substance are zeolite crystals impregnated with calciumchloride.